root:
             product   file:plan.py
             product   step:./plan.py

file:plan.py
               state = CONFIRMED
             creator   root:
                sink   step:./plan.py

step:./plan.py
               state = SUCCEEDED
                need = PLAN
           using_env = STEPUP_PATH_FILTER [dynamic]
             creator   root:
              source   file:plan.py
             product   file:a_input.txt
             product   file:b_input.txt
             product   file:c_input.txt
             product   file:d_input.txt
             product   step:cp -p a_input.txt out/a.txt
             product   step:cp -p b_input.txt solo.txt
             product   step:cp -p c_input.txt out/optional.txt
             product   step:cp -p d_input.txt exact_optional.txt

file:a_input.txt
               state = CONFIRMED
             creator   step:./plan.py
                sink   step:cp -p a_input.txt out/a.txt

file:b_input.txt
               state = CONFIRMED
             creator   step:./plan.py
                sink   step:cp -p b_input.txt solo.txt

file:c_input.txt
               state = CONFIRMED
             creator   step:./plan.py
                sink   step:cp -p c_input.txt out/optional.txt

file:d_input.txt
               state = CONFIRMED
             creator   step:./plan.py
                sink   step:cp -p d_input.txt exact_optional.txt

step:cp -p a_input.txt out/a.txt
               state = SUCCEEDED
                need = TARGET (implied by sinks > DEFAULT)
             creator   step:./plan.py
              source   file:a_input.txt
             product   file:out/a.txt
                sink   file:out/a.txt

file:out/a.txt
               state = BUILT
             creator   step:cp -p a_input.txt out/a.txt
              source   step:cp -p a_input.txt out/a.txt

step:cp -p b_input.txt solo.txt
               state = SUCCEEDED
                need = TARGET (implied by sinks > DEFAULT)
             creator   step:./plan.py
              source   file:b_input.txt
             product   file:solo.txt
                sink   file:solo.txt

file:solo.txt
               state = BUILT
             creator   step:cp -p b_input.txt solo.txt
              source   step:cp -p b_input.txt solo.txt

step:cp -p c_input.txt out/optional.txt
               state = PENDING
                need = OPTIONAL
             creator   step:./plan.py
              source   file:c_input.txt
             product   file:out/optional.txt
                sink   file:out/optional.txt

file:out/optional.txt
               state = PLANNED
             creator   step:cp -p c_input.txt out/optional.txt
              source   step:cp -p c_input.txt out/optional.txt

step:cp -p d_input.txt exact_optional.txt
               state = SUCCEEDED
                need = TARGET (implied by sinks > OPTIONAL)
             creator   step:./plan.py
              source   file:d_input.txt
             product   file:exact_optional.txt
                sink   file:exact_optional.txt

file:exact_optional.txt
               state = BUILT
             creator   step:cp -p d_input.txt exact_optional.txt
              source   step:cp -p d_input.txt exact_optional.txt
